This invention relates to earth satellite communication systems and, more particularly, to a system for broadcasting regional information over a satellite communication system.
Mobile satellite communication systems are used for transmitting point-to-point voice and data communications using a constellation of satellites, such as low earth orbit (LEO)) or medium earth orbit (MEO) satellite constellations. Such systems may include a number of user terminals, several terrestrial ground stations or gateways, and a number of satellites for bi-directionally coupling the user terminals to terrestrial telecommunication networks, such as the Public Switched Telephone Network (PSTN), and the Internet via the gateways.
The point-to-point communications are generally those conducted between a single one of the user terminals and another user terminal, or a terrestrial wired or wireless telephone, or a data processor modem (for data calls as opposed to voice calls.)
Known in this regard are satellite communication systems with satellites having multi-beam antennas that are used to produce multiple spot beams to illuminate particular areas on the Earth. Specifically, a satellite receives a Forward Beam Uplink from a communication gateway and provides a number of Forward Beam Downlinks, by means of the spot beams, over a defined footprint area on the ground. Such a system can be used to facilitate the transmitting of point-to-point communications between satellite user terminals and other terminals and telephones around the world.
While point-to-point communication links are very important, it would also be desirable to provide a point-to-multipoint or broadcast capability, particularly on a regional basis, as this would enable important local information, such as weather, traffic, addresses of local services and vendors, and emergency information, to be provided simultaneously to a number of user terminals. This regional content can be broadcast as audio messages or as data messages to be displayed on the user terminal.
It is thus an object and advantage of this invention to fully utilize the capabilities of a modern mobile satellite communication system by providing an ability to also broadcast regionally related information.
It is a further object and advantage of this invention to disseminate broadcast information based on a Static Orthogonal Code Tiling Technique that separates a broadcast services from point-to-point communication services that make Duse of the same satellite system.
The present invention is directed to fully utilizing the capabilities of a communication satellite constellation, in particular one that uses Code Division, Multiple Access (CDMA) and multiple spot beams, by providing an ability to broadcast regionally related information within a satellite spot beam. The broadcast of the regionally related information can be made on a scale of the beam spot size divided by the number of orthogonal spreading codes (e.g., Walsh Codes) and the frequencies available for use.
More particularly, the invention uses a simplifying scheme to disseminate broadcast information based on a Static Orthogonal Code Tiling Technique that separates the broadcast services from the point-to-point communication services, and make use of the same satellite system. Each broadcast region may be on the order of 1% of the satellite beam size. The technique involves a static Frequency/Walsh Code tiling over the Earth""s surface, and a user terminal at a given position tunes to an appropriate (for that location) predetermined frequency and Walsh Code to receive information broadcast from a satellite over a forward beam downlink. The gateway first receives the broadcast information, such as regional traffic messages, from a ground-based entity referred to herein for convenience as a Broadcast Processing Center. The methods of implementation of the Broadcast Processing Center are varied and not particularly germane to the invention described in this patent application.
A dedicated Frequency Division Multiplex (FDM) channel of a CDMA-based system is preferred to be used to disseminate the regionally dependent messages from the gateways to the user terminals. The use of the dedicated FDM channel eliminates much of the synchronization and power control that would be required from sharing a frequency channel with a system used for point-to-point communications. This technique thus avoids the need for a pilot signal, as the user terminal has a priori knowledge of the required frequency and code pair required to access the desired broadcast channel(s), and the resulting system can co-exist with a point-to-point, call-by-call communication system, and may make use of the same satellite constellation and ground infrastructure.
A method is disclosed for operating a satellite-based telecommunications system. The method includes steps of: (A) tiling at least a portion of the surface of the Earth in accordance with a static Frequency/Walsh Code tiling; (B) storing information descriptive of the tiling; (C) operating a satellite user terminal so as to determine its current location; (D) associating the current location of the user terminal with a Frequency/Walsh Code, based on the stored information; and (E) further operating the satellite user terminal to acquire, using the Frequency/Walsh Code, a desired broadcast communication signal that is transmitted in a satellite forward downlink beam.
For a non-geosynchronous satellite case, wherein the satellite forward link beam moves relative to a point on the ground, the method further includes a step of handing off at least the Walsh Code from the first satellite forward downlink beam to a second satellite forward downlink beam due to motion of the first satellite forward downlink beam away from the current location of the user terminal.